Calcium-calmodulin-dependent mechanisms accelerate calcium decay in gastric myocytes from Bufo marinus.
1. [Ca2+] was recorded in voltage-clamped gastric myocytes from Bufo marinus. Repolarization to -110 mV following a 300 ms depolarization to +10 mV led to triphasic [Ca2+]i decay, with a fast-slow-fast pattern. After a conditioning train of repetitive depolarizations the duration of the second, slow phase of decay was shortened, while the rate of decay during the third, faster phase was increased by 34 +/- 6% (mean +/- S.E.M., n = 21) when compared with unconditioned transients. 2. [Ca2+]i decay was biphasic in cells injected with the calmodulin-binding peptide RS20, with a prolonged period of fast decay followed by a slow phase. There was no subsequent increase in decay rate during individual transients and no acceleration of decay following the conditioning train (n = 8). Decline of [Ca2+]i in cells injected with the control peptide NRS20 was triphasic and the decay rate during the third phase was increased by 50 +/- 19% in conditioned transients (n = 6). 3. Cell injection with CK3AA, a pseudo-substrate inhibitor of calmodulin-dependent protein kinase II, prevented the increase in the final rate of decay following the conditioning train (n = 6). In cells injected with an inactive peptide similar to CK3AA, however, there was a 45 +/- 17% increase after the train (n = 5). 4. Inhibition of Ca2+ uptake by the sarcoplasmic reticulum with cyclopiazonic acid or thapsigargin did not prevent acceleration of decay. 5. These results demonstrate that [Ca2+]i decay is accelerated by Ca(2+)-calmodulin and calmodulin-dependent protein kinase II. This does not depend on Ca2+ uptake by the sarcoplasmic reticulum but may reflect upregulation of mitochondrial Ca2+ removal.
McGeown
J G
JG
School of Biomedical Science, Queen's University of Belfast, UK. g.mcgeown@qub.ac.uk
McCarron
J G
JG
Drummond
R M
RM
Fay
F S
FS
D000818:Animals; D002024:Bufo marinus; D002118:Calcium / Q000378:metabolism* / Q000502:physiology*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002147:Calmodulin / Q000502:physiology*; D004558:Electric Stimulation; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005753:Gastric Mucosa / Q000166:cytology / Q000378:metabolism*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D012519:Sarcoplasmic Reticulum / Q000201:enzymology
D002147:Calmodulin; D004791:Enzyme Inhibitors; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D000252:Calcium-Transporting ATPases; D002118:Calcium